It is increasingly common to pay for things electronically. However, you still want the children to know about money, and what it all means. So practice counting money at home. Have the child make a small purchase using their own money.
For the older ones, teach them about budget, and to write down and keep track of all the receipts. It is easy for us to overspend when using credit cards, so a person on the Autism spectrum could go through their money really quickly and then have nothing. All this has to be taught, over and over again until it sticks.